1. Field of the Invention
The present invention relates generally to an injection molding machine system, and more particularly to a power supply system for an injection molding machine.
2. Description of the Background Art
FIG. 3 is a block diagram showing how a conventional power supply is performed in a molding plant in which a motor-driven injection molding machine is operated. Referring to FIG. 3, a substation 1 disposed in a plant PLNT is supplied with high-voltage commercial electric power from outside, wherein the electricity is stepped down to an actually-utilized voltage. The stepped-down electric power in supplied via a power supply line PSLY extending from a power supply wire network 2 in the plant to an injection mechanism of an injection molding machine body 52, a servo-motor for driving a mold clamping mechanism and a drive unit of a peripheral device 53 through a control device 51 or each motor-driven injection molding apparatus 5. Further, other molding-related devices such as a die carrying apparatus 4 are supplied with the electric power.
A power generation equipment 3 for backup is provided in a comparatively-large-scale plant PLNT, wherein a power generation command is given when it is unable to utilize the external power source due to some accident, thereby preventing a stoppage of the production by supplying the electric power for a fixed period of time.
The motor-driven injection molding apparatus 5 shown in FIG. 3 includes a plurality of servo-motors together with an injection mechanism and a molding clamping mechanism, wherein all the servo-motors are driven during a cycle time that lasts several tens of seconds through several minutes. Especially in an injection operation and a mold opening/closing operation, a quick start and a sudden stop are performed at every cycle, and therefore a consumption of the electricity increases to a great degree. Moreover, a consumption of the electricity for a heater of a heating cylinder is not ignorable. It is therefore required that a necessary quantity of total electric power be sufficiently prepared.
In a configuration of the conventional plant illustrated in FIG. 3, if the power supply from the external commercial power source is cut off due to some accident, the power supply from the power supply line PSLY is likewise cut off. In such a case, the control device can instantaneously cope with the power cut-off by use of a backup power source in the case of executing the information processing and storing the data.
There arises, however, such a problem that the instantaneous coping is impossible with respect to the heater and the servo-motors which consume a large quantity of electricity and perform the mechanical operations. This is because the power generation equipment 3 is not always operated in the normal case. Therefore, the power generation equipment 3 is incapable of supplying the electric power as a substitute for the commercial electric power immediately after an occurrence of the accident. Therefore, the drive of the servo-motors related to the mechanical operations and the heating by the heater comes to a uncontrolled state at that point or time.
As a result, a molded product in the making might be hardened as it stays in a die assembly, or a molten resin might be hardened as it resides in a gate and a nozzle member, or the molten resin might be scattered from an abutting surface of the die assembly when the clamping state of the die assembly is slackened, resulting in such a problem that the normal operation can not be promptly restarted even when the state of the power supply is restored normally.
Moreover, if the supplied voltage temporarily descends due to a small short-circuit fault in the plant and simultaneous start-ups of the respective devices in a state where demands for the electricity is close to a limit of supply as in the summer in addition to the case where the commercial power supply is temporarily cut off because of the accident, etc. as described above, the drive of the servo-motor for the motor-driven injection molding machine is not performed as the program instructs. This results in such a problem that the molded product having a predetermined quality can not be obtained.
The injection molding machine has an aspect of process control of molding the molten resin by controlling movements of the mechanical components such as the die assembly, an injection screw, etc. and controlling a temperature, and therefore comes to suffer a serious damage if the power supply falls into an unstable state for even a short period of time.
What has been discussed so far is an example in the case of the plant including the power generation equipment. In the case of a small-scale molding plant including one single or several injection molding machines, however, there is almost no case of its being provided with non-utility power generation equipment. Such a plant depends on only the commercial electric power, and there arise the same problems as those aforementioned.
Further, in the case of a hydraulic drive system injection molding machine also, the same problems are caused by the stoppage of the power supply to a variable capacity pump, a variety of switch values, a motor for driving this pump and so on.